Zero VOC aqueous dispersion of an acid-modified polyolefin and a monoepoxide/polymeric acid adduct

ABSTRACT

An acid-modified polyolefin is dispersed in water by adding a hydroxy-functional ester made from a polymeric acid and a monoepoxide having from 14 to 46 carbon atoms to the water. Said dispersion is substantially zero-VOC. When a composition of this invention is applied to the surface and cured by baking the article at an elevated temperature, a coating is obtained which improves the adherence of subsequent coatings to a polyolefinic article. A polyolefinic article is one having a surface comprising polypropylene or a polypropylene modified with rubber called a thermoplastic polyolefin (TPO).

BACKGROUND OF THE INVENTION

This invention relates to aqueous dispersion of an acid-modifiedpolyolefin and an adduct of a monoepoxide with a polymeric acid. Moreparticularly, it relates to a coating composition which is an aqueousdispersion of an acid-modified polyolefin or acid-modified chlorinatedpolyolefin and a hydroxy-functional ester of a monoepoxide with apolymeric acid. When said dispersion is applied to the surface of apolyolefinic article and cured by baking the article at an elevatedtemperature, it improves the adherence of subsequent coatings to thearticle. Still more particularly, this invention relates to aqueousdispersions which are substantially free of volatile organic compounds(zero VOC).

The use of polypropylene and polypropylene-containing compounds modifiedwith rubber called thermoplastic polyolefins (TPO) and other polyolefinshas grown significantly in areas such as the automotive market since the1970's because of their low cost, low weight, impact resistance, ease ofmolding and recyclability. They have been used in interior applicationssuch as airbag covers and exterior ones such as fascia and trim. Becauseof their low surface energy and non-polar nature, however, an articlehaving a polyolefinic resin on its surface is very difficult to paintwith decorative and/or protective coatings. This surface must bephysically or chemically altered to render it paintable with availablecoating technology. A common approach to the painting of polypropyleneand TPO is the use of an adhesion promoting primer coating that uses achlorinated polyolefin resins to gain adhesion to the surface. Thesecoatings are easy to process in a production environment and can betopcoated after a short ambient flash or bake. However, solvent bornechlorinated polyolefin resins are sprayed at V.O.C.'s of 5.7 pounds pergallon or higher to properly coat the surface of the polypropylene orTPO. Because of increased environmental concerns, much effort has beendirected to the problem of reducing the pollution caused by theevaporation of solvents from such coating compositions. Part of theseefforts has been the development of new coating formulations whicheliminate or at least diminish the emission of organic solvent vaporsinto the atmosphere. The dispersion of halogenated polyolefinic resinsin water using conventional surfactants is taught in InternationalPublication No. WO 90/12656.

Aqueous coating compositions comprising a dispersion of a polymer and aneutralized water-dispersible reaction product of an epoxy resin with apolymer containing carboxyl groups are taught by Chu et al in U.S. Pat.No. 4,446,258. A volatile organic solvent is used to dissolve thecarboxyl-group containing polymer, the epoxy resin, and an amine so thatthe reaction takes place in solution. The ionic polymer thus preparedwith the exemplary epoxy resins of Chu et al will not disperse anacid-modified polyolefin as defined herein.

Polymeric acids, as defined herein, are incompatible with saidacid-modified polyolefins and cannot be used to disperse them in water.It has been found that the incompatibility of acid-modified polyolefinsand the polymeric acids may be overcome for the purposes of dispersionof such polyolefins in water by using the hydroxy-functional ester madefrom such a monoepoxide and the polymeric acid as a dispersant. Theresultant aqueous dispersion may be used as a coating composition forarticles having a polyolefinic surface. The ester of the polymeric acidis a dispersant that cannot be leached out of a coating by water ororganic solvents. The resultant primer coating in combination withconventional topcoats, moreover, has good water resistance and solventresistance.

SUMMARY OF THE INVENTION

It is an object of this invention, therefore, to provide a zero VOCaqueous dispersion of an acid-modified polyolefin and an adduct of amonoepoxide with a polymeric acid.

It is a related object of this invention to provide an aqueous, zero VOCcoating composition which promotes adhesion of a subsequent coating to apolypropylene-based substrate.

It is another object of this invention to provide such a coatingcomposition containing a dispersant which is non-leachable from theresultant coating by water or an organic solvent.

It is another object of this invention to provide a coating compositionin which both carboxyl- and hydroxyl functional sites for crosslinkingare available.

It is another object of this invention to provide a coating compositionwhose versatility of formulation is similar to that of conventionalwater-based acrylic compositions.

It is another object of this invention to provide a coating compositionhaving improved wetting and recoating characteristics.

It is another object of this invention to provide an article having apolypropylene-based surface which is coated with an aqueous, zero VOCcoating composition containing a resin which, upon drying, promotesadhesion of a subsequent coating to the surface.

The above objects and other objects which will become apparent from thefollowing description thereof are provided by an aqueous compositioncomprising a neutralized aqueous dispersion of an acid-modified polyolefin and an adduct of a monoepoxide having from 14 to 46 carbon atoms witha polymeric acid having a molecular weight of from about 1000 to about20,000, preferably from about 3000 to about 7000.

DETAILED DESCRIPTION OF THE INVENTION

To facilitate the description and claiming of this invention, the termacid-modified polyolefin means an acid-modified polyolefin, anacid-modified chlorinated polyolefin, and mixtures thereof. They areeither totally free of hydrophilic functional groups which would renderthem dispersible in water or their hydrophilic character is of suchsmall degree as to have the same result.

A halogen-free, acid-modified polyolefin of this invention is acopolymer of a higher α-olefin and at least one monomer selected fromthe group consisting of ethylene and propylene, said copolymer having anα,β- unsaturated dicarboxylic acid, an anhydride, or half ester thereofgrafted thereon. The olef in copolymer is a random copolymer or blockcopolymer of the ethylene and/or propylene with a higher α-olefin. Ahigher α-olefin is one having from 4 to 8 carbon atoms. Examples of thehigher α-olefins include, butene-1, pentene-1, and hexene-1.Propylene/α-olefin copolymers suitable for use in this invention areavailable from Eastman Chemical Products, Inc. and from the RexeneCompany. Ethylene/α-olefin copolymers suitable for use in this inventionare available from Union Carbide under the trademark FLEXIMERS. They areexemplified by ethylene/butene, ethylene/hexene, andethylene/butene/hexene copolymers.

The acid-modified chlorinated polyolefin of this invention is derivedfrom a chlorinated polyolefin having a molecular weight of from 5000 to30,000 and a chlorine content of from about 10 to about 30 weightpercent. Said chlorinated polyolefin may be prepared according to knownmethods such as described in U.S. Pat. No. 4,070,421 which is herebyincorporated herein by reference. Chlorinated polyolefins are availablecommercially from Eastman Chemical Products and from Toyo Kasei KogyoCo. Ltd.

The acid modification of the polyolefin and chlorinated polyolefin isaccomplished by grafting it with maleic anhydride or maleic acid oranother α,β-unsaturated dicarboxylic acid, an anhydride thereof, or ahalf ester thereof. Suitable acids for that purpose are exemplified byfumaric acid, itaconic acid, citraconic acid, allylsuccinic acid,mesaconic acid and aconitic acid, and their acid anhydrides. The amountof α,β-unsaturated dicarboxylic acid or the like is from about 1 toabout 20% by weight of the grafted copolymer. If over 20% by weight, thegrafting efficiency decreases.

Grafting of a α,β-unsaturated dicarboxylic acid, an anhydride or halfester thereof onto the polyolefin may be conducted by a known methodwherein the polyolefin is liquified by heating it above its meltingpoint and the grafting is conducted in the presence of a freeradical-generating agent such as a organic peroxide.

When using this method, a reactor equipped with an intensive agitator,Banbury mixer, kneader, extruder or the like may be employed and anα,β-unsaturated dicarboxylic acid, its acid anhydride, or its half esterand a radical-generating agent (e.g., benzoyl peroxide) or a solutionthereof in a low boiling solvent are added at a temperature of fromabout 150° C. to about 300° C.

The number average molecular weight (determined by gel permeationchromatography or GPC) of the halogen-free polyolefin after beinggrafted with the α,β-unsaturated dicarboxylic acid or its acid anhydrideis from about 3000 to 55,000. If over 55,000, dispersion into waterbecomes difficult because of high viscosity.

Maleated amorphous copolymers of propylene and hexene, of propylene andbutene, and of propylene, butene, and ethylene that are suitable for thepurposes of this invention are available from Eastman Chemical Products,Inc.

For the purposes of this invention, the term polymeric acid means acopolymer of acrylic and/or methacrylic acid and suitable co-monomers.Suitable co-monomers include styrene, vinyl acetate, vinyl chloride,vinylidene chloride, acrylonitrile, ethyl acrylate, butylmethacrylate,and similar acrylate esters. Copolymers of styrene and/or α-methylstyrene and acrylic acid and/or methacrylic acid are examples. Thepolymeric acid has a number average molecular weight of from about 1000to about 20,000, preferably from about 3000 to about 7000 and an acidnumber of from about 180 to about 240. The upper limit on the molecularweight is determined by the processability of the resulting ester. Drygrade polymers (i.e., containing less than 7 by weight of residualsolvent) are preferred so that substantially solvent-free dispersionsare produced in accordance with this invention. Polymers of this typeare available from Morton International, Inc. and B. F. Goodrich, amongothers.

The monoepoxides suitable for this invention are represented by theformula ##STR1## wherein R is an alkyl radical, an alkoxy radical, analkylphenoxy radical, or an alkenylphenoxy radical, the alkyl, alkoxy,and alkenyl moieties each having from 12 to 40 carbon atoms. The choiceof the monoepoxide is determined by the nature of the resin to bedispersed in water. Examples of the monoepoxides suitable for thisinvention include epoxidized α-olefins containing a total of from 14 to30 carbon atoms. They are prepared by reacting α-olefins with organicperoxides such as peracetic acid or perbenzoic acid, or other peroxidessuch as hydrogen peroxide as described, for example, in U.S. Pat. No.3,404,163. For some uses, such as promoting the adhesion of subsequentcoatings to a polyolefinic substrate, the epoxidized α-olefin preferablycontains from 14 to 18 carbon atoms. Examples of such epoxidizedα-olefins include 1,2-epoxytetradecane, 1,2-epoxyhexadecane, and1,2-epoxyoctadecane, and mixtures of two or each of the three. They arecommercially available from Union Carbide Corporation. Amonoepoxy-polybutene having a molecular weight of about 350 and sold byAldrich Chemicals also exemplifies the monoepoxides useful for thisinvention, as do the epichlorohydrin adducts of monohydric alkylphenols,alkenylphenols, and long chain alcohols.

The esterification of the polymeric acid with the monoepoxide may beconducted by heating and stirring a mixture of the two reactants at fromabout 230° to about 360° F. (˜110-182° C.) until the monoepoxide issubstantially consumed. The weight ratio of the reactants is from about10:90 to about 70:30, preferably at least about 20:80, equal amountsbeing more preferred. A preferred temperature is from about 300° toabout 320° F. Completeness of the reaction may be observed by monitoringthe acid number as it decreases throughout the reaction to approach thetheoretical value based on the ratio of epoxy equivalents to acidequivalents in the reaction mixture. The reaction time ranges from aboutone to two hours. The desired polymeric, hydroxy-functional ester havingan acid number of from about 50 to about 150, preferably from about 70to about 110, is obtained.

The dispersion of the hydrophobic, acid-modified polyolefin in water isaccomplished by mixing it with the hydroxy-functional ester of thepolymeric acid at a temperature of from about 200° to about 230° F.(˜90-110° C.) for about 30 minutes and then adding water and ammoniumhydroxide or other base such as sodium hydroxide, potassium hydroxide,methylamine, ethylamine, propylamine, butylamine, hexylamine,octylamine, ethanolamine, propanolamine, diethanolamine,N-methyldiethanolamine, dimethylamine, diethylamine, triethylamine,N,N-dimethylethanolamine, 2-dimethylamino-2-methyl-1-propanol,2-amino-2-methyl-1-propanol and morpholine. The use of organic amines issuitable only when the introduction of small amounts of VOC must betolerated in order to achieve other desirable properties.

Neither conventional, low molecular weight surfactants nor co-solventsare necessary for dispersing the acid-modified polyolef in. Aqueousdispersions of acid-modified polyolefin resins that are substantiallyfree of volatile organic compounds are preferred but a V.O.C. greaterthan zero pounds per gallon may be tolerated in accordance with thisinvention for special effects. A conventional surfactant may be used,also, when a special effect is desired.

The polyolefin surface may be that of an article made from a polyolefinor it may be that of a film on an article made from another material.The articles of particular interest for the purposes of this inventionare polypropylene-based automotive parts that may be exposed to highhumidity and may be subject to repeated contact with gasoline.

Pigments such as conductive carbon black, talc and other organic andinorganic pigments may be employed.

The invention is described in further detail in the following examples.

Grafting of Polyolefin with Maleic Anhydride Example A

In a four-neck flask fitted with agitator, condenser and droppingfunnel, 250 g of a propylene-butene copolymer (70 mol % propylene; M_(n)25,000; melt viscosity 8500 mPA.sec at 190° C.) sold as REXENE E-21 waxwas liquefied by heating it to 430° F. (˜220° C.). Then, keeping thetemperature of system at 220° C., 20 g of maleic anhydride and 8 g of5-di(t-butylperoxy) hexane in 15 g of methyl ethyl ketone (MEK) wereadded dropwise over one hour while agitating, and the reaction wascontinued for 0.5 hour. After the reaction, MEK was removed by flow ofnitrogen and the acid grafted olefin copolymer (6% maleic anhydride byweight) was recovered after cooling. The number average molecular weightwas 8000 when measured by GPC.

Example B

By a procedure similar to Example A, 20 g of maleic anhydride and 8 g of5-di-(t-butyl peroxy)hexane in 15 grams of MEK were reacted with 250 gof EASTOFLEX D-174 propylene-hexene copolymer (propylene component 64mol %; M_(n) 55,000. melt viscosity 4000 centipoises at 190° C.) toobtain an acid grafted olefin copolymer (5.1% by weight grafted maleicanhydride). The number average molecular weight (CPC) of the product was15,000.

Dispersion of Polymeric Acid in Water EXAMPLE 1

A mixture of forty grams of a styrene/acrylic acid copolymer having anacid number of 210 and sold by Morton International, Inc. under itstrademark and product number MOREZ 101 LS and 25 grams of1,2-epoxyhexadecane (UNION CARBIDE EPOXIDE C-16) was stirred and heatedat 290° F.(˜143° C.) for one hour to give a hydroxy-functional esterhaving an acid number of 54 and then 60 parts of the modified polyolefinof Example A was added; this mixture was stirred and heated at 290°F.(143° C.) for 0.5 hour. After cooling the mixture to 210° F., a heatedsolution of 20 grams of concentrated ammonium hydroxide (28% ammonia) in20 grams of water was added and then 260 grams of water at 200° F. wasadded to give an opaque dispersion.

EXAMPLE 2

A mixture of 80 grams of a styrene/acrylic acid copolymer having an acidnumber of 235 and sold by Morton International, Inc. under its trademarkand product number MOREZ 300 and 25 parts of 1,2-epoxyhexadecane werestirred and heated at 310° F. (˜154° C.) for one hour and then cooled to230° F. (110° C.) to give a hydroxy functional ester; 80 grams of achlorinated polyolefin EASTMAN CP 343-1) was added and this mixture wasstirred and heated at that temperature for 10 minutes. After cooling themixture to 210° F., a heated solution of 15 grams of concentratedammonium hydroxide (28% ammonia) in 15 grams of water was added and then270 grams of water at 200° F. was added to give a dispersionsatisfactory for the purposes of this invention.

EXAMPLE 3

CARBOSET-1250 styrene/acrylic acid copolymer (acid number 235, B. F.Goodrich Company) (40 grams) and 25 grams of 1,2-epoxyhexadecane weremixed and heated at 310° F. for one hour to produce a hydroxy functionalester having an acid number of 60; 60 parts of PETROLITE KNF-26 modifiedpolyolefin having an acid number of 58 (a copolymer of propylene andhexene-1 grafted with an isopropyl half ester of a maleic anhydride)were mixed with the hydroxy functional ester at that temperature for 0.5hour. After cooling the mixture to 210° F., a heated solution of 20grams of concentrated ammonium hydroxide (28% ammonia) in 20 grams ofwater was added and then 290 grams of water at 200° F. was added to givea viscous dispersion which is satisfactory for the purposes of thisinvention.

EXAMPLE 4

A mixture of 50 grams of MOREZ 300 styrene/acrylic copolymer having anacid number of 235 and 25 grams of polybutylene epoxide (molecularweight 365; ALDRICH) were mixed and heated at 310° F. for four hours toproduce a hydroxy functional ester having an acid number of 110; 32.5grams of an acid-modified, chlorinated polyolefin (MITSUBISHI RAYONS-645) was mixed into the hydroxy functional ester at that temperaturefor 10 minutes. After cooling the mixture to 210° F., a heated solutionof 15 grams of concentrated ammonium hydroxide in 15 grams of water and132 grams of hot water was added at about 200° F. to give a dispersionhaving a 40% non-volatile content.

EXAMPLE 5

A mixture of 40 grams of MOREZ 300 styrene/acrylic copolymer and 20grams of 1,2-epoxyhexadecane was stirred at 310° F. (154° C.) for twohours to give the hydroxy functional ester having an acid number of 87and was then cooled to 230° before 80 grams of the modified polyolefinof Example B was added; this mixture was stirred at 230° for 10 minutes.A solution of 15 grams of concentrated ammonium hydroxide in 15 grams ofwater was added to the mixture at 210° and then 300 grams of water wasadded at 200° to give a satisfactory dispersion for the purposes of thisinvention.

In the following examples, adhesion promoting thermoset coatings for apolypropylene-based surface were prepared and tested. The weight percentof all components marked with one or two asterisks is given in terms ofsolids present.

    ______________________________________                                                       Concentration (Wt %)                                           Component        Example 6                                                                              Example 7                                           ______________________________________                                        Prod. of Example 2                                                                             22.8     --                                                  Prod. of Example 5                                                                             --       20.8                                                Water            73.2     74.6                                                Ammonium hydroxide                                                                             0.3      0.3                                                 Thixotrope*      2.5      2.5                                                 Wetting agent    0.2      0.2                                                 CYRACURE**       0.6      1.0                                                 PTSA*.sup.†                                                                             0.4      0.1                                                 ______________________________________                                         **Union Carbide trademark for a cycloaliphatic diepoxide curing agent         .sup.† ptoluene sulfonic acid                                     

After thorough mixing of the components, the coating compositions ofExamples 6 and 7 were sprayed at approximately 60 psi onto separate TPOsubstrates to build a film of from 0.3 to 0.5 mil. The coated substrateswere baked at 120° C. for approximately 10 minutes. After the bakingcycle, the coated substrates were cooled to room temperature and thenpainted with a basecoat and a clearcoat, both of which weresolvent-based, melamine-curing, thermosetting paints. A second TPO parthaving the cured coating of Example 7 on it was painted with anisocyanate-curing basecoat and clearcoat. Each of the painted parts wasair dried at room temperature for about 10 minutes and themelamine-curing paint was baked at 120° C. for 30 minutes and theisocyanate-curing paint was baked at 82° C. for 30 minutes.

Adhesion of the paints to the coated substrates of this invention wasdetermined by cross-hatch adhesion testing. The test consisted ofcutting the painted surface with a fine cutter to form one hundred (100)cross-cuts at intervals of 1 mm each. After pressing a cellophane tapeonto the painted surface and peeling it off at an angle of 180°, thenumber of remaining cross-cuts were counted. The results are given inTABLE 1.

Resistance of the painted parts to gasoline and to 100% relativehumidity was also tested. Separate parts painted as described above werescribed with an X and then immersed in a synthetic gasoline consistingof 45% toluene and 55% VM&P naphtha by weight. Loss of paint wasdetermined visually. Results are given in TABLE 1. Another set of partswas painted as described above and each painted part was X-scribed andplaced in a cabinet held at 100% R.H. and 38° C. for 240 hours. Adhesionwas tested by the tape pull described above. Results are given in TABLE1.

                  TABLE 1                                                         ______________________________________                                        Coating/    Paint       Gasoline Humidity                                     paints      adhesion    resistance                                                                             resistance                                   ______________________________________                                        Ex. 6/melamine                                                                            10          10       10                                           Ex. 7/melamine                                                                            10          10       10                                           Ex. 6/isocyanate                                                                          10          10       10                                           ______________________________________                                         0 = poor                                                                      10 = excellent                                                           

With this description of the invention in detail, those skilled in theart will appreciate that modification may be made to the inventionwithout departing from the spirit thereof. Therefore, it is not intendedthat the scope of the invention be limited to the specific embodimentsthat have been illustrated and described. Rather, it is intended thatthe scope to the invention be determined by the scope of the appendedclaims.

What is claimed is:
 1. An article having a polyolefin resin surfacecovered with a coating comprising a cured mixture of an acid-modifiedpolyolefin and a hydroxy-functional ester of a monoepoxide with apolymeric acid; said monoepoxide having from 14 to 46 carbon atoms andthe general formula: ##STR2## wherein R is an alkyl radical, an alkoxyradical, or an alkylphenoxy radical; and said polymeric acid having anumber average molecular weight of from about 1000 to about 20,000 andan acid number of from about 180 to about 240 .
 2. The article of claim1 wherein the molecular weight of the polymeric acid is from about 3000to about 20,000.
 3. The article of claim 2 wherein the molecular weightof the polymeric acid is from about 3000 to about 7000 .
 4. The articleof claim 1 wherein the alkyl, alkoxy, and alkenyl moieties each havefrom 12 to 40 carbon atoms.
 5. The article of claim 1 wherein themonoepoxide is an epoxidized α-olefin having from 14 to 30 carbon atoms.